1. Field of the Invention
The present invention relates to a method for the production of nanocarbon which comprises subjecting a low hydrocarbon such as methane as a raw material to catalytic reaction so that the raw material is directly decomposed to produce nanocarbon and hydrogen and a catalytic reaction device for producing nanocarbon.
2. Description of the Related Art
As a device for producing nanocarbon from a low hydrocarbon as a raw material there has been heretofore known a carbon dioxide fixing device as disclosed in JP-A-10-182121. This fixing device is intended to fix mainly carbon dioxide using methane and carbon dioxide as raw material. This fixing device employs a process for producing carbon and water using an existing reaction called Bosch reaction. This device also employs a fluidized bed process to effect continuous reaction. In this process, carbon grown on a catalyst and the catalyst are continuously separated and withdrawn by a so-called centrifugal separation process.
In general, chemical reactors using a catalyst can be roughly divided into three types, i.e., fixed bed type, moving bed type, fluidized bed type. In all these types of chemical reactors, the catalyst doesn't change itself with reaction. However, the process for the production of nanocarbon involving the reaction of a low hydrocarbon in the presence of a catalyst (hereinafter referred to as “present process”) is a catalytic reaction process by which as the reaction proceeds, a functional nanocarbon grows with a fine metal catalyst used as top, causing the rise of the volume of the catalyst itself. Therefore, when the fixed bed process is used in the present process, the reaction space is gradually filled with and blocked by grown carbon, preventing the raw material gas from flowing therethrough and hence disabling continuous reaction to disadvantage. Ordinary moving beds are essentially used mainly in large-sized combustion devices such as stoker furnace. The reaction at the step of combusting a combustible material with excessive air involves exothermic reaction that proceeds continuously. However, the application of ordinary moving bed process to the present process, which involves endothermic reaction, results in the deterioration of reaction efficiency and energy efficiency that adds to cost. Further, the fluidized bed process requires that the distribution of particle size of catalyst in the bed be optimized to keep the fluidized state optimum. In the present process, however, the volume and weight of catalyst change with time, making it difficult to control the distribution of particle size of catalyst in the bed.
It is therefore necessary that the catalyst which is continuously growing be withdrawn using a fluidized bed provided with a centrifugal separating machine as in the process disclosed in JP-A-10-182121. It is also necessary that when the raw material gas is used also as a fluidic gas in the case where the catalyst bed is suspended or turned, the gas flow rate needs to satisfy both the fluidization optimization conditions and the reaction optimization conditions. However, the present process reaction doesn't proceed so fast. SV value of the raw material gas is preferably as low as possible. On the other hand, in order to use cyclone or make gyration flow, the gas flow rate needs to be higher than that required to attain SV value for optimum reaction. It is thus made difficult for the aforementioned centrifugal separation type fluidized bed to make efficient practice of the present process. Further, the fluidized bed requires a large-sized apparatus that adds to construction cost. Therefore, it is usual that catalytic reactions which can never be effected in other processes are effected in fluidized bed process.